JP patent publication 10-336929 discloses an electric machine. A plurality of seat plates are arranged on a circumference of a yoke at intervals in the circumferential direction and fastened with first bolts to the yoke. Magnet pieces are placed on the seat plates and a laminate obtained by laminating thin steel plates is placed as a pressing member on the magnet pieces. The magnet pieces are clamped between the laminate and the seat plates by the fastening force of second bolts. The magnet pieces, the laminate, the seat plates and the second bolts include a magnetic block.
U.S. Pat. No. 6,879,075 discloses a permanent magnet synchronous machine. A circumferentially oriented rotor assembly is provided with alternating permanent magnets and magnetic pole pieces. In order to reduce the amount of leakage flux in the rotor and increase the effective length of the permanent magnet, a trapezoidal or otherwise tapered permanent magnet structure is used. By alternating trapezoidal permanent magnet and magnet pole pieces, a higher intensity magnetic field is created in the air gap utilizing the same radial space in the motor without altering the weight or volume of the motor compared to known machines.
U.S. Pat. No. 3,567,974 discloses a permanent magnet electric machine. FIG. 4 shows permanent magnet blocks fastened between wedge-shaped pole cores and abutment members. The abutment members form conjointly with the iron structure of the rotor a supporting star structure into which the permanent magnets and the pole cores are placed. The pole cores are fastened with non-ferromagnetic screws to the rotor.